Handling Unit2(VEKP-EXIDV2) is over writing with Handling Unit1(VEKP-EXIDV)

Hello LE experts,

We have an issue with Handling Unit2(VEKP-EXIDV2). 

We are raising a PO to the external vendor. Vendor will create a Sales Order with ref to our PO and then create a Outbound Delivery.

When vendor do the Outbound delivery, Inbound Idoc will create automatically in our system through EDI which creates an Inbound Delivery and update to the PO in our SAP system.

In Inbound Idoc we have HU2(VEKP-EXIDV2) information which means the vendor handling unit. Now the issue is, when Inbound delivery is creating by Inbound Idoc, HU2(VEKP-EXIDV2) is over writing with HU1(VEKP-EXIDV) which is not correct.

I need an help how this HU2(VEKP-EXIDV2) is over writing with HU1(VEKP-EXIDV) and how to correct it.

Thanks in advance for the help